Friday, 19 October 2012

Beware of November/December cold but does it continue into Jan and Feb?

We are seeing a lot of variablility from the modelling in terms of what we can expect this winter. A few things to take note of on the current SST pattern is the very warm water off the east coast of north america and near greenland. 
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This will promote lower pressures off the east coast causing cold sinking air from northeastern canada to move southwards to take the place of the warm rising air to the east. This will cause a thermal gradient to set up between cold air building across canada and warm water in the atlantic. A clash of air masses will cause more storminess to develop in the east with a trough favoured along the east coast. Ridging will be centred further north and east across greenland. Notice the cooling of SST's that has taken place near iceland which supports the blocking idea and promotes troughiness across the region.

On the pacific side we see many signals supporting a cold winter. The core of coldest anomalies have shifted towards the bering sea and warmer temperature anomalies are showing up northeast of hawaii. Here are september's anomalies to compare to.
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This promotes a trough in the bering sea, a negative EPO pattern, a ridge off the west coast as thicknesses will average higher in this area with lower thicknesses further northwest. This will cause an ULL feature to develop across the bering sea and this will be very key when it comes to cold developing in the east. A ridge in the west favours a +PNA pattern and phasing across the ohio valley and eastern and central great lakes as opposed to areas further east(when ridge is centred in the rockies). This is good news for snow lovers across southern ontario and quebec and based on current storm track trends this month( the LRC pattern setting up for this january) and favourable SST's I think the storm track may be centred further west then most are expecting for this winter. The major warming of the SST's of the west coast is good news for winter weather lovers. The worst case scenerio that may develop is the cooling of the atlantic SST's and west coast SST's favoring a western trough and this situation should continue to be monitored. We have seen some cooling of the extreme warmth in the atlantic but that is to be expected at this time of year. The warming of the anomalies off the west coast is enough to counter the atlantic effects. 

Another thing that must be kept in mind is the cooling of the east pacific SST's but keep in mind that the nino 4 SST's are still above normal. West based el ninos produce a much colder weather pattern then an east based el nino. Many people are stressing over the fact that the el nino may be under performing but what must be kept in mind is the fact that the ENSO regions have warmed considerably since last winter and it is the change in the SST pattern that will cause the response to cold in north america this winter as long as the coldest anomalies stay centred west. Also to take note of is the warm pool located beneath the surface near the date line. Current cross section shows this.
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Some other years with very similar trends are 2009,2003,2002 and 2004. Here is the combined analog package for winter.
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We need to keep an eye on the MJO wave to see if this water can move up to the surface and possibly regenerate the el nino (a strong wave would favour warming in the ENSO regions). Current MJO wave is headed for strong phases 1 and 2 and this is backed but the strengthening easterlies which would help to bring the warm water to the surface.
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Look how the wind has changed to much more easterly.
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So as we can see the current SST pattern are very favourable for cold in the east and if it were to hold would set up as a top 5 winter. This is why i think this november is going to be cold with an early start to the lake effect season. We have seen the evidence of what this SST setup can bring with the major cold shots in august,september and the beginning of october. November looks to start of cold with a trough in the east and a persistent west based block. I believe that another strong cold shot like we haven't seen yet this fall is coming down during november much like the october outbreak but one month later with more strength. I think you will see that the GFS and Euro ensembles will want to hold onto the cold for longer because of this but right now ensemble member uncertainty is causing a weaker trough to show up on the modelling especially because it is far into the long range. With our current SST's I believe a very cold november and december are coming up and we will get a ridge developing along the west coast (watch out for big snowstorms along the st lawrence and into ontario) as gulf moisture is picked up and pushed northwards. The problem might be what this pattern does to our SST's in the second half of winter that could change the amazing pattern right now. This needs to be watched very carefully. Here is the cpc sst analog model which bases it predictions on current SST's.
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Years with a september AMO within 0.5 of this years and an above normal tropical end game in the atlantic basin(similar to this year).

December starts cold but it shows how a favourable pattern can come back to bite you.
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JAN:
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FEB:
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DJF:
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